Tuning structure



March 4f,v 1941.

R. B. AYER 4 TUNING STRUCTURE Filed May 27, 1939 WENSWQN im INVENTOR. RA YMOND B. AYER ATTORNEY.

Patented Mar. 4, 1941 UNiTED STATES PATENT QFFICE TUNING STRUCTURE Ware Application May 27, 1939, Serial No. 276,118

4 Claims.

My invention relates to high power high frequency radio circuit structures, particularly to apparatus such as Shortwave transmitters.

Alternating currents of ultra-high radio frequencies ilowon the surface of their conductors, the depth of penetration of the currents into the conductor, or skin effect, being so pronounced at frequencies in the range of 60 megacycles per second that the -two sides of a sheet of metal are in effect electrically insulated for such high frequency currents and the current can pass from one side of the sheet to the other only by flowing to and around the edge of Ithe sheet. Because of this phenomenon the high frequency anode current of a conventional cylindrical anode must now over .the rim of the anode, thereby increasing the length and impedance of the anode circuit. These currents, when of high magnitude, heat the metal at the rim of the anode and are particularly troublesome in tubes where glass is sealed to the rim of the anode as in the usual water-cooled types.

The object of my invention is to provide a high frequency circuit structure for radio tubes in which the impedance of the anode circuit and the heating at the rims of connected anodes are minimized.

The characteristic features of my invention are defined in the appended claims and one preferred embodiment is described in the following specification and shown in the accompanying drawing in which Figure 1 shows in plan View two tubes connected in Ipush-pull with the novel circuit structure of my invention, Figures 2 and 3 are, respectively, end andside views of the structure of Figure 1, and Figures 4 and 5 are top and end views of one shorting bar embodying rmy invention.

For purpose of illustration, two tubes, each of the type shown in the Zottu et al. Patent No. 2,113,671, April 12, 1938, are mounted side-byside and are connected for push-pull operation. Each tube comprises a cylindrical metal anode 2 sealed at each end, in the particular tubes shown, to a glass bulb 3 through .the ends of which are sealed the lead-in conductors for the cathode and grid electrodes. Intermediate the ends of the bulbs are sealed in screen grid lead-in rings 4 and the anodes may, if desired, be enclosed in metal water-cooling jackets. Tuned transmission lines connect the two anodes in push-pull resonant circuits, the lines shown in Figure 1 comprising parallel metal arms 5 extending laterally in both directions from the plane throughthe centers of the two tubes. The arms are parallel (Cl. Z50- 27) straight at strips of metal secured to the opposing sides of the anodes.

The arms connecting the two anodes comprise a resonant circuit which may be tuned to any desired frequency by adjusting their electrical length. The circuit of the arms may conveniently be tuned by adjusting the distance of shorting bar 6 from the anodes. The shorting bars, preferably transverse plates, contact the inner faces of the arms with spring wipers, are moved along the arms by a threaded rod l, and the two shorting bars may be kept at uniform distances from the anode by right hand and left hand threads on the rod. A load may be coupled to the tubes by direct connections to the anode or by in ductive coupling to the tank.

Because ultra high frequency current flows only on the surface of its conductors and flows only along paths of the lowest impedance and shortest around the rim of the anode to lessen the localI heating and reduce the resistance to the flow of current. According to my invention lthe current is distributed around the periphery of the anode near the anode rim by a sheet metal flange 9 preferably integral with the edges of the arm.

and extended outwardly from the arm around the anode and joined to the anode in good electrical contact by clamps or by brazing or soldering. The flange may be tapered from its Widest point opposite .the anode .to a narrow rib or iin I0 at' the outer ends of the arms, the contour of the flange being determined by the current distribution lbetween the anode and the shorting bar. The ends of the arms may be made into a one piece structure, and may conveniently be stilfened by the fins extended to the ends'of the structure.

The reinforced armsmay bear the weight of the tubes, and since no alternating current iiows in the arms beyond the shorting bars, the entire tube and tuning structure may -be conveniently supported upon insulators Il at points removed from high frequency potentials.

In operation high frequency current flows along the faces of the anges and the arms and across the shorting bars. T'he flanges surrounding the anodes, distribute the current to the rims-of the anodes and prevent the concentration of current and heating. My novel ano'de-to-cincuit connection not only decreases the temperature of the anode-to-glass seals, but decreases the mean length of the path for high frequency current, and reduces .the impedance of the anode circuit. The symmetrical double :circuit of the structure shown with arms extending to both sides of the anodes parallels the circuit inductance and increases the length of the external circuit avail.- able f-or tuning.

While the arms are preferably flat rectangular metal pieces with flanges and ns for strength .and are secured tangentially against Ithe opposed sides of the anodes for closer'spac-ing and higher capacity, the arms may if -desired be pipes, rods or bars extending rtangentially or radially from the sides of the anodes. By adjustingthe shor-ting bar to a distance from .the anodes equal to an odd multiple of a quanter-w-avelength of the operating frequency, standing waves are produced on the arms with a :current maximum anda voltage node at the shorting bar. My improved tank circuit can, of course, be used with single-ended tubes where only one end of the anode is sealed to a glass bulb. Y

While the circuit ,structure shown in Figures 1, 2 :and 3 is symmetrical ,with respect to the plane through the centers Vof ,the two tubes, .it will be obvious to those skilled in the art thatthe tank circuit may be extended in one direction only from. said plane. In such an arrangement flanges 9 would extendfrom the tuning'arms 5 and encircle .the anodes .at lleastone-half way around the adjacent side vof .the anode.

In transmitters designed for radiating considerable amounts of high frequency power, the problem of making g'ood electrical Contact between the shorting bar 6 and the tuning arm 5 may yconveniently be solved as shown in Figure 4 where the body of the bar carries a rectangular piece of thin sheet `metal vI2, such :as copper, curled into a loop along its `edges and held in rm contact with the inner face of the arms 5 by spring pressed blocks L3. The pressur-e 'applied by the blocks I3 may be made as high as practical -by springs i4 :consistent with easyl sliding of the bar along the faces of the tuning arms 5.

' Since most of the resistance of the tuning Icircuit is lumped at :the contacting area between the arms `and the shorting bar, the principal heating caused Iby the current is at the bar. This heat may be conveniently `dissipated by vertical cooling fins l5, preferably integral with the shorting bar and extending outwardly from its rear face. To obtain Ia good heat transfer from sheet I2 to the radiating fins lthe sheet is preferably soldered or brazed to the inner face of theshorting bar. Naturally or :artificially circulated air through the fins may serve to keep the shortingbar at reasonable #temperatures` f ing said anode and in good electrical contact with the outer wall of fthe anode, the sole support for Y said electron discharge device being supporting insulators at the outerfendsof said strip.

2. Two electron discharge devices with cylindrical anodes, a structure for operating said devices at frequencies at which the current of the operating frequency does not penetrate the wal-l of said anode, comprising two parallel straight, fiat strips of metal -secured to opposing sides of eachA of anodes and extending laterally from the plane through .the centers of the `anodes, said strips kbeing electrically coup-led, means for uniformlydistributing said -current along the rim of each anode'as i-t flows between the anode and its vstrip and for stiffe'ning the strip comprising a'ilaterally extending lian-ge on each of said strips surrounding and good contact with the anodes,

-adjacentouteri ends of said strips being joined and supported on Aain-insulator.

3. A circuit structure 'for electro-n discharge devices comprising an electronv discharge vdevice with a Icylindrical anode, a tuning element for said device v`comprising two rigid arms-'extending laterallyinopposite directions! from the anode, each of said arms being longer .than one-quarter of a .wavelength at theoperating frequency and being secured to' said anode in a unitary mechanical structur-e, the sole support for said tuning element Vand its attached electron -idischarge device comprising an electrical insulator joined to each arm at its outer end.- A

1 .4."` Acircuit structure for-electron discharge devices comprising 'two'parallel straight iiat strips of metal, 'an adjustable snorting bar between 'said strips :comprising a rectangular blockbetween and transverse to the planes of saidfstrps, a rectangular piece of -thin sheet metall attached, in 'good heat transfer relation, rto one side of said block, 'said piece of sheet metal being approximately coextensive with' .the width of saidstrips, the edgesofisaidv sheet metal being curled into loops and 'slidably engaging said strips throughout 'the width lof said strip, means for holding the loops Yin f contact with Ysaid strips comprising a plurality of side-by-side spring pressed plungers in the edges of said block bearing ragainst, ,the inner surfaces of said loops. f

.; j RAYMOND naviera.` 

